Extravert vs introvert leadership: which one is more effective?

In his lecture "Leading Quietly", included in the Wharton Leadership Conference 2012, organizational psychologist (and teacher in Wharton Business School)Adam Grant presents his conclusions after several works and studies analyzing the behavior of leaders either with an extravert or introvert personality and the situations where one or the other works more effectively, thus examining alternative ways to put leadership into practice and to convey motivating messages to the rest of the team.

Adam Grant's theses are based on a classification of population along an axis between introversion and extraversion, similar to the one used in Myers-Briggs test. To illustrate it during the lecture, he mentions the different levels of stimulation needed by an introvert or extravert person in order to feel "fully engaged" or, using the term coined by Mihaly Csikszentmihalyi, "in the flow". In these terms, an overstimulation makes the introvert feel "burned out" and an understimulation makes the extravert feel bored.The most relevant conclusion in Adam Grant's studies is that, although statistics show a very high percentage of organizational leaders scoring in the extravert (or even "very extravert") side of the axis, extravert leadership tends to be ineffective with proactive workers, which precisely is the most demanded kind of worker in the present context. Adam Grant explains that extravert leaders tend to feel "threatened" when they receive ideas and suggestions from the rest of their team, because the feeling of being the center of attention is what makes these leaders feel "in the flow", and therefore tend to react in a slightly more defensive way when faced with a proactive team member. This has the double effect of (1) demotivating team members from making contributions, because they perceive their suggestions are not being valued correctly, and (2) demotivating leaders from looking for a global benefit in those contributions. On the other hand, a team member with a "good follower" style tends to perceive an extrovert leader in a more positive way.Adam Grant links the concept of "leading quietly" (i.e. a more introvert and quiet leadership) and its potential benefits to the idea of leading through integrity/example and "leading by doing", co-doing tasks with the rest of the team instead of just telling them how to do them. It also relates it the novel concept of "outsourcing inspiration", proposing that team leaders are not the only ones who should provide the rest of the team with motivational messages, and that there may be external sources who might convey them in much more effective ways.

Here is the video containing the lecture (duration: 52:47). I would highlight the 10-minute section between 15:40 and 25:06 time marks, where Adam Grant presents the main core of his theses:

It is a pity that the camera is focused on Adam Grant during the whole lecture, as it seems clear that being able to see the projected slides would be really useful in some moments (e.g. when the audience is asked to do some tests projected on the screen). To solve this, Adam Grant himself later published a short video showing the slides used in his presentation, to follow it in a more effective way: